Ryanair pilots in Germany will strike for 24 hours on Friday, their union said on Wednesday, adding to action planned in Ireland, Sweden and Belgium.

Dutch pilots' union VNV is also considering calling strikes on Friday but has not yet taken a decision.

Ryanair operates from 86 bases in 37 countries and carried 130 million passengers last year, making it Europe's largest airline by that measure.

Below are a list of the strikes that have taken place or are planned since union negotiations began.

Aug. 10:

The Irish airline had already cancelled 146 flights for Friday as a result of strikes planned in Ireland, Sweden and Belgium. The 250 cancellations from the German strike takes the total to just under 400 flights, or about 17 percent of the more than 2,400 flights it has scheduled across Europe for that day.

Aug. 3:

Irish pilots stage a fourth one-day strike, causing Ryanair to cancel 20 flights. The airline has responded to the Irish action by cutting its winter fleet there by 20 percent and putting over 300 employees on preliminary notice. [L5N1UU456]

July 31:

Pilots in the Netherlands back the Dutch Airline Pilots Association call for industrial action in a vote the unions calls a necessary "wake up call" in negotiations.

July 25/ 26:

Cabin crew in Italy, Spain, Portugal and Belgium staged a two-day strike that forced Ryanair to cancel the flights of more than 50,000 customers, the airline's biggest-ever strike.

July 24:

Ryanair cancelled 16 of around 2,300 daily flights on after the third one-day strike by Irish pilots.

July 20:

Ryanair cancelled 24 of around 2,300 daily flights after a second one-day strike by Irish pilots.

July 12:

Around a quarter of Ryanair's 350 pilots bases in its home country of Ireland went on strike for the first time in a push for better conditions.

March 29:

Ryanair cancelled dozens of flights to and from airports in Portugal when cabin crew staged three one-day strikes on March 29, April 1 and April 4.

Feb. 10:

Three Italian unions representing mainly cabin and ground crew staged a four-hour strike because they were not included in contract negotiations with Ryanair.

Dec. 22:

Ryanair was unable to avert its first ever pilots strike on December 22 when pilots in Germany held a four-hour walkout but with little impact on flights.

(Reporting by Graham Fahy; Editing by Padraic Halpin/Keith Weir)